1. Field of Invention
This invention relates to tire building drums, and more specifically, to a tire building drum incorporating an expandable and collapsible cylindrical deck upon which a tire or part of a tire carcass may be formed.
2. Description of the Related Art
Tires, such as for example radial automotive tires of the type having an inner liner, a plurality of body plies, sidewalls, and a plurality of beads disposed proximate an inner circumference of the tire, are known in the art. It is understood generally that in traditional tire manufacture, following initial preparation of various components to be used, a generally cylindrical tire carcass is built through a process of assembling various components of a tire onto one or more tire building drums. Such tire carcasses normally include tire components such as multiple plies of tire bands, yarns, and one or more annular reinforcing tire beads at opposite ends of the tire bands. Thereafter, the tire carcass is expanded to a toroidal shape with the plies of tire bands forming an outer circumference of the toroid and the tire beads forming inner circumferences of the toroid. Often additional material is added to the tire carcass to form an uncured or “green” tire. The green tire is then formed into a desired finished geometry and cured, often through a process commonly known as “vulcanization,” to allow the tire to retain the finished geometry. For convenience herein, reference will be made simply to “tire building” and to a “tire,” it being understood that these terms are intended to embrace the construction of sub-assemblies such as a tire carcass, belt and tread package, etc.
One apparatus and method useful in expanding a tire carcass to a toroidal shape is a tire shaping drum of the type discussed in U.S. Pat. No. 4,325,764, issued to Appleby et al. (hereinafter “the '764 patent”). In the '764 patent, a tire carcass is placed over a tire shaping drum having a pair of segmented, radially expandable and contractible annular support structures, each support structure defining a radially expandable and contractible beadlock for establishing a firm frictional connection between the support structure and a reinforcing bead of the tire carcass. The annular support structures defining the beadlocks are adjustably repositionable in relation to one another along an axial dimension of the tire shaping drum to assist both in mating the beadlocks to the reinforcing beads of the tire carcass and in shaping the tire carcass to a toroidal shape. The device of the '764 patent is configured to allow injection of air or other fluid between the tire carcass and a portion of the tire shaping drum between the beadlocks to allow the tire carcass to be expanded to a toroidal shape.
In other tire shaping drums, a plurality of substantially rigid deck segments are provided between the support structures of the tire shaping drums. The deck segments are configured to be radially movable in relation to a central shaft of the tire shaping drum between an expanded position and a collapsed position. In the expanded position, the deck segments are arranged in an end-to-end fashion to define an outwardly facing cylindrical or toroidal working surface defining a desired expanded shape of a tire carcass positioned on the drum. In the collapsed position, the deck segments are positioned in a radially-inwardly collapsed position, thereby allowing an expanded tire carcass to be removed from the tire shaping drum and a new tire carcass to be positioned on the tire shaping drum. The deck segments of the tire shaping drum are carried from a hub rotatable with a main support/drive shaft of the drum. The interconnection between the hub and the deck segments can take a number of forms, but one convenient form utilizes pivoting links which are operated by movement of a drive component of the hub relative to the remainder of the hub to move the links between collapsed and expanded positions carrying the deck segments with them.
It will be recognized that in a conventional drum, in order to ensure that the deck segments are circumferentially aligned in their expanded positions, extreme accuracy in the construction and operation of the link mechanisms and circumferential clearance between deck segment edges are needed. Accordingly, it is difficult to produce such drums with a large range of movement between collapsed and fully expanded positions. Moreover, it is difficult to control the lateral and radial positions of the deck segments, when in their expanded positions, and thus it is difficult to control lateral and radial run-out of the expanded drum. Accordingly, there is a need in the art for a tire building drum in which the aforementioned difficulties are minimized or obviated.